Photosensitive self-assembled monolayer for selective placement of hydrophilic structures

ABSTRACT

A photosensitive monolayer is self-assembled on an oxide surface. The chemical compound of the photosensitive monolayer has three components. A first end group provides covalent bonds with the oxide surface for self assembly on the oxide surface. A photosensitive group that dissociates upon exposure to ultraviolet radiation is linked to the first end group. A second end group linked to the photosensitive group provides hydrophobicity. Upon exposure to the ultraviolet radiation, the dissociated photosensitive group is cleaved and forms a hydrophilic derivative in the exposed region, rendering the exposed region hydrophilic. Carbon nanotubes or nanocrystals applied in an aqueous dispersion are selectively attracted to the hydrophilic exposed region to from electrostatic bonding with the hydrophilic surface of the cleaved photosensitive group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/541,231, filed Aug. 14, 2009, which is divisional of U.S. patentapplication Ser. No. 11/870,167, filed Oct. 10, 2007, now U.S. Pat. No.7,732,119, issued on Jun. 8, 2010, the entire contents of which areincorporated herein by reference.

The present invention was made with U.S. Government support underContract No. N66001-06-C-2047 awarded by Defense Advanced ResearchProjects Agency (DARPA).

BACKGROUND

The present invention generally relates to methods forming a patternedsurface containing a hydrophobic region and a hydrophilic region,methods of selective placement of carbon nanotube and a nanocrystal onthe patterned surface, photosensitive compounds for forming such apattern, and structures containing a self-aligned carbon nanotube or ananocrystal.

With the realization that end of scaling for conventional CMOSintegrated circuits is fast approaching in the semiconductor industry,alternative nanostructures and materials have been investigated. Of suchnanostructures and materials, carbon nanotubes (CNTs) offer excellentintrinsic properties that are suitable for high performance nanoscaledevices. Research in the replacement of semiconductor based field effecttransistors and optoelectronic devices and sensors with carbon nanotubebased nanoscale devices has been producing promising results in thisfield.

A key advantage of CNTs over conventional CMOS devices is that scalinglimitations of MOSFETs due to boundary scattering of electrons fromimperfect interfaces are solved naturally in CNTs which have a smooth,well coordinated graphene structure with no bonds to the outside. Thisenables CNTs to retain excellent transport properties to much smallerlateral dimensions than silicon. The small radius and possibility ofcompletely surrounding the CNT by a gate provide excellent electrostaticconfinement of channel electrons, enabling the channel length to bescaled down to very small dimensions, and their small size would enablehigh packing densities.

Although single, isolated CNT based field effect transistors and otherdevices have been demonstrated, many challenges remain in theconstruction of an integrated circuit employing CNTs as an activematerial. One such challenge is reliable placement of CNTs on asubstrate surface with alignment, i.e., placement of the CNTs in apredefined region for fabrication of a CNT based device.

Several methods for selective placement of CNTs on a surface have beendisclosed in the prior art. An exemplary prior art method employs thesteps of:

prepatterning the surface into a metal oxide region and a silicon oxideregion;

applying alkylphosphonic acids or alkylhydroxamic acids on theprepatterned surface, wherein the alkylphosphonic acids oralkylhydroxamic acids self-assemble on the silicon oxide region, whilenot assembling on the metal oxide region; and

applying functionalized CNTs on the prepatterned surface containing thepatterned alkylphosphonic acids or alkylhydroxamic acids, wherein thefunctionalized CNTs are selectively attracted to the metal oxide region.

The exemplary prior art method has the drawback of requiring at leastone lithographic step for formation of the metal oxide region and thesilicon oxide region, in which a photoresist needs to be applieddirectly on the surface to be patterned, thus making the cleaning ofresidual photoresist material from the surface difficult and therebydegrading the effectiveness and fidelity of the pattern to be formed onthe surface.

In view of the above, there exists a need for a method for patterning asurface into hydrophobic regions and hydrophilic regions without directcontact of a photoresist with the surface so that residual material fromthe photoresist does not produce adverse effects on the pattern, and achemical compound for effecting such a method.

BRIEF SUMMARY

The present invention addresses the needs described above by providing amethod for patterning a surface into hydrophobic regions and hydrophilicregions without direct contact of a photoresist with the surface, and achemical compound for effecting such a method.

A photosensitive monolayer is self-assembled on an oxide surface, whichmay be a metal oxide surface or a semiconductor oxide surface. The oxidesurface may, or may not be patterned. The chemical compound of thephotosensitive monolayer has three components. A first end groupprovides covalent bonds with the oxide surface for self assembly on theoxide surface. A photosensitive group that dissociates upon exposure toultraviolet radiation is linked to the first end group. A second endgroup linked to the photosensitive group provides hydrophobicity. Theself-assembled monolayer of the photosensitive compound is initiallyhydrophobic without ultraviolet radiation. Upon exposure to ultravioletradiation, the dissociated photosensitive group is cleaved and forms ahydrophilic derivative in the exposed region, rendering the exposedregion hydrophilic. Carbon nanotubes applied in an aqueous dispersionare selectively attracted to the hydrophilic exposed region to fromelectrostatic bonding with the hydrophilic surface of the cleavedphotosensitive group, enabling patterning of the carbon nanotubeswithout direct contact of a photoresist with the oxide surface.Hydrophilic nanocrystals may also be patterned in the same manner.

According to an aspect of the present invention, a structure isprovided, which comprises a patterned monolayer located on an oxidesurface of a substrate;

wherein the patterned monolayer contains a first contiguous region of afirst material and a second contiguous region of a second material, andwherein the first contiguous region and the second contiguous regionlaterally abut, and do not overlie, each other;

and wherein the first material includes:

a first end group that forms covalent bonds with the oxide surface;

a photosensitive group that dissociates upon exposure to ultravioletradiation linked to the first end group; and

a second end group having hydrophobicity and linked to thephotosensitive group;

and wherein the second material includes:

said first end group; and

a third end group linked to the first end group and havinghydrophilicity and derived from the photosensitive group by dissociationof a link by ultraviolet radiation.

In one embodiment, the structure comprises at least one carbon nanotubelocated directly on the second contiguous region and not overlying thefirst contiguous region.

In another embodiment, the structure further comprises at least onenanocrystal located directly on the second contiguous region and notoverlying the first contiguous region. The nanocrystal may be a metalnanocrystals such as gold or palladium or a semiconducting nanocrystalor an oxide nanocrystal.

In even another embodiment, the first end group comprises one ofhydrogen, fully or partially fluorinated alkyl, fully or partiallyfluorinated alkoxy, or fully or partially fluorinated alkylthio, andwherein a total number of carbon atoms in said alkyl, alkoxy, or saidalkylthio is from 1 to 20.

In yet another embodiment, the oxide is a metal oxide, wherein the metalis selected from elemental metals and an alloy thereof.

In still another embodiment, the oxide is a compound of a semiconductormaterial and oxygen, and wherein the semiconductor material is one ofsilicon, germanium, carbon, and an alloy thereof.

According to another aspect of the present invention, a photosensitivecompound is provided, which comprises:

a first end group that forms covalent bonds with the oxide surface;

a photosensitive group that dissociates upon exposure to ultravioletradiation linked to the first end group; and

a second end group having hydrophobicity and linked to thephotosensitive group.

In one embodiment, the photosensitive compound forms a self-assembledmonolayer on a metal oxide.

In another embodiment, the assembled monolayer of the photosensitivecompound transforms, upon irradiation with ultraviolet light, into amonolayer having a carboxylic acid end group.

According to yet another aspect of the present invention, a method ofmanufacturing a structure is provided, which comprises:

providing a substrate containing an oxide surface;

applying a monolayer of a photosensitive material to said oxide surface;wherein the photosensitive material includes:

a first end group that forms covalent bonds with the oxide surface;

a photosensitive group that dissociates upon exposure to ultravioletradiation linked to the first end group; and

a second end group having hydrophobicity and linked to thephotosensitive group; and

lithographically exposing a region of the monolayer to ultravioletradiation, wherein the photosensitive group in the exposed regiondissociates upon exposure to said ultraviolet radiation and forms athird end group rendering the surface hydrophilic.

In one embodiment, the exposed region laterally abuts, and does notoverlie, an unexposed region of the monolayer, and wherein the unexposedregion is not exposed to the ultraviolet radiation, and wherein theexposed region and the unexposed region collective constitute a patternof a hydrophobic surface and a hydrophilic surface.

In another embodiment, the method further comprises selectively placingat least one carbon nanotube or at least one nanocrystal on the pattern,wherein the at least one carbon nanotube is preferentially placed overthe exposed region.

In even another embodiment, the at least one carbon nanotube or the atleast one nanocrystal is deposited from organic solvents or aqueoussolutions containing surfactants.

In yet another embodiment, the at least one carbon nanotube isfunctionalized with acid-terminating functionality or amine-terminatingfunctionality and is deposited from an aqueous solution or an aqueousalcohol solution.

In still yet another embodiment, the nanocrystal is a gold nanocrystal,a palladium nanocrystal, or a semiconducting nanocrystal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1-4B are sequential vertical cross-sectional views of an exemplarystructure employing a monolayer of a photosensitive material forpatterning a hydrophobic surface and a hydrophilic surface.

FIGS. 5A-5D are the chemical structures of compounds employed in themanufacture of 4-diethylphosphonatomethyl benzoic acid chloride, whichis the compound of FIG. 5D according to a first embodiment of thepresent invention.

FIG. 6 is the chemical structure of 4-substituted 2-nitrobenzyl alcoholemployed in the first embodiment of the present invention.

FIG. 7 is the chemical structure of the photosensitive phosphonic acidaccording to the first embodiment of the present invention.

FIG. 8 is the chemical structure of the photosensitive phosphonic acidas attached to an oxide surface according to the first embodiment of thepresent invention.

FIG. 9 is the chemical structure of a derivative of the photosensitivephosphonic acid upon exposure to ultraviolet radiation to form ahydrophilic surface and as attached to an oxide surface according to thefirst embodiment of the present invention.

FIGS. 10A and 10B are the chemical structures of compounds employed inthe manufacture of 4-substituted 2-nitrobenzyloxycarbonyl chloride,which is the compound of FIG. 10B according to a second embodiment ofthe present invention.

FIG. 11 is the chemical structure of 4-aminomethylbenzoic acid accordingto the second embodiment of the present invention.

FIG. 12 is the chemical structure of a carbamate according to the secondembodiment of the present invention.

FIG. 13 is the chemical structure of a photosensitive hydroxamic acidaccording to the second embodiment of the present invention.

FIG. 14 is the chemical structure of photosensitive hydroxamic acid asattached to an oxide surface according to the first embodiment of thepresent invention.

FIG. 15 is the chemical structure of a derivative of the photosensitivehydroxamic acid upon exposure to ultraviolet radiation to form ahydrophilic surface containing an amine end group and as attached to anoxide surface according to the first embodiment of the presentinvention.

FIG. 16A is an atomic force micrograph of a lithographically ultravioletradiation exposed sample containing a monolayer of photosensitivephosphonic acid. FIG. 16B is a magnified view of an exposed regionshowing presence of carbon nanotubes therein. FIG. 16C is a magnifiedview of a masked region showing absence of any carbon nanotubes therein.

FIGS. 17A and 17B are scanning electron micrographs of functionalizedcarbon nanotubes deposited on a photosensitive monolayer of4-trifluoromethyl photosensitive phosphonic acid, which was patterned byselective ultraviolet irradiation.

DETAILED DESCRIPTION

As stated above, the present invention relates to methods forming apatterned surface containing a hydrophobic region and a hydrophilicregion, methods of self-alignment of a carbon nanotube and a nanocrystalon the patterned surface, photosensitive compounds for forming such apattern, and structures containing a self-aligned carbon nanotube or ananocrystal. It is noted that like and corresponding elements arereferred to by like reference numerals.

The following terms are employed herein:

As defined herein, the term “alkyl”, alone or in combination with anyother term, refers to a straight-chain or branch-chain saturatedaliphatic hydrocarbon radical containing a number of carbon atoms from 1to 20, preferably from 1 to 10 and more preferably from 1 to 5 carbonatoms. Examples of alkyl radicals include, but are not limited to,methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,tert-butyl, pentyl, isoamyl, n-hexyl and the like.

As defined herein, the term “alkoxy”, alone or in combination with anyother term, refers to —O-alkyl, wherein alkyl is as defined above.

As defined herein, the term “alkylthio,” alone or in combination withany other term, refers to —S-alkyl, wherein alkyl is as defined above.

Referring to FIG. 1, an exemplary structure according to the presentinvention comprises a substrate 100 and a monolayer 200 of aphotosensitive material. The substrate 100 may comprise an insulatormaterial, a semiconductor material, or a metallic material. The topsurface of the insulator material which contacts the monolayer 200 ofthe photosensitive material comprises an oxide surface which may containa metal oxide or a semiconductor oxide. The metal oxide contains atleast one elemental metal. The semiconductor oxide is a compound of asemiconductor material and oxygen, and wherein the semiconductormaterial is one of silicon, germanium, carbon, and an alloy thereof.

The monolayer 200 of the photosensitive material is attached to theoxide surface by covalent bonds. The photosensitive material comprisesthree groups. A first end group 210 forms covalent bonds with the oxidesurface which contains the at least one elemental metal in the case ofthe metal oxide or the semiconductor material such as silicon in thecase of the semiconductor oxide. The first end group 210 may comprise acarboxylic acid, a phosphonic acid or, a hydroxamic acid. Thephotosensitive group 220 is linked to the first end group. Thephotosensitive group 220 dissociates upon exposure to ultravioletradiation. The photosensitive group 220 may comprise a nitribenzylmoiety having a photosensitive bond such as a CO—O—CH₂ bond or aCH₂—NH—CO bond. A second end group 230 is linked to the photosensitivegroup 220 and provides hydrophobicity to the photosensitive material.The second end group 230 may comprise one of hydrogen, fully orpartially fluorinated alkyl, fully or partially fluorinated alkoxy, orfully or partially fluorinated alkylthio, and wherein a total number ofcarbon atoms in said alkyl, alkoxy, or said alkylthio is from 1 to 20.

The covalent bonds between the first end group 210 in each molecule ofthe photosensitive compound and the oxide surface enables self-assemblyof the photosensitive material on the oxide surface as the monolayer200. This is because the covalent bond is formed only between the acidicend group of photosensitive material and the oxide surface. In otherwords, the molecules of the photosensitive material does not provideatom available for covalent bonding except for those that are bonded tothe oxide surface.

Referring to FIG. 2, the exemplary structure is subjected to a patternedbeam of ultraviolet radiation. A conventional lithography tool and aconventional lithographic mask may be employed to generate the patternedbeam of ultraviolet radiation. Application of a photoresist onto thesubstrate 100 is not necessary since the monolayer 200 of thephotosensitive material reacts with the patterned beam of ultravioletradiation.

The photons of the patterned beam of ultraviolet radiation react withthe photosensitive group 220 to dissociate the photosensitive group 220within the exposed region of the monolayer 200 of the photosensitivematerial. As the photosensitive group 220 dissociates by the ultravioletradiation, the second end group 230 having hydrophobicity is removedalong with some atoms of the photosensitive group 220. The remainingportion of the photosensitive group 220 forms a derivative of thephotosensitive group 220 having an exposed hydrophilic functionality.After removal of the cleaved portion containing the second end group230, for example, in an aqueous or aqueous alcohol solution, the exposedportion of the monolayer 200 containing the exposed photosensitivematerial has a hydrophilic surface.

Referring to FIG. 3, the monolayer 200 is thus patterned and contains atleast a first contiguous region 310 and at least a second contiguousregion 320. The monolayer 200 may contain another first contiguousregion 310′ and/or another second contiguous region (not shown).Typically, the monolayer 200 constitutes a plurality of first contiguousregions (310, 310′) and a plurality of second contiguous regions 320,each containing a plurality of molecules. Since the monolayer 200contains a single layer of material, the first contiguous region 310 andthe second contiguous region 320 laterally abut, and do not overlie,each other. The first contiguous region 310 comprises the photosensitivematerial. The second contiguous region 320 has a lithographic dimensionand comprises a derivative of the photosensitive material. Thederivative of the photosensitive material comprises:

the first end group 210; and

a third end group 240 linked to the first end group 210 and havinghydrophilicity and derived from the photosensitive group 220 bydissociation of a link by ultraviolet radiation.

Referring to FIG. 4A, at least one carbon nanotube 400 is preferentiallyplaced on the second contiguous region 320 (See FIG. 3) of the monolayer200. Carbon nanotubes are applied to the surfaces of the monolayer 200as a dispersion of carbon nanotubes in an organic solvent or an aqueoussolution. Since the first contiguous regions (310, 310′; See FIG. 3) hasa hydrophobic surface and the second contiguous region 320 has ahydrophilic surface, the carbon nanotubes are repulsed from the secondcontiguous region 320 and attracted to the first contiguous regions(310, 310′). Thus, the placement of the at least one carbon nanotube 400on the substrate 100 may be patterned without employing a conventionalphotoresist that contacts the substrate 100.

Referring to FIG. 4B, the exemplary structure in FIG. 3 may alternatelybe employed for self-assembly of nanocrystals 500 containing hydrophilicsurfaces. The nanocrystals 500 may have dimensions from about 1 nm toabout 100 nm. The nanocrystals 500 that may be patterned in this mannerinclude, but are not limited to, a gold nanocrystal, a palladiumnanocrystal, or a semiconducting nanocrystal. As in the case of thecarbon nanotubes, the nanocrystals 500 are repulsed from the secondcontiguous region 320 and attracted to the first contiguous regions(310, 310′). Thus, the placement of the nanocrystals 500 on thesubstrate 100 may be patterned without employing a conventionalphotoresist that contacts the substrate 100.

The following are two embodiments of synthesizing the photosensitivematerial employed to form the monolayer 200, which do not limit thescope of the present invention.

Embodiment 1 Synthesis of Photosensitive Phosphonic Acids

According to embodiment 1, or a first embodiment, of the presentinvention, a mixture of methyl 4-bromomethylbenzoate, of which thechemical formula is shown in FIG. 5A, and triethyl phosphate is formedand heated at an elevated temperature. For example, 10 grams of methyl4-bromomethylbenzoate and 40 grams of triethyl phosphate may be mixedand heated at 120° C. for 4 hours. The solution is cooled and excesstriethyl phosphite may be evaporated under reduced pressure to form alight yellow oil, which is methyl diethylphosphonatomathyl-benzoate, ofwhich the chemical formula is shown in FIG. 5B. Methyldiethyl-phosphonatomathylbenzoate in the form of the light yellow oilmay be used without further purification in the next step.

Methyl diethylphosphonatomathylbenzoate is then dissolved in methanoland lithium hydroxide is added to the solution. For example, 10 grams ofmethyl diethylphosphonatomathyl-benzoate may be dissolved in 50 ml ofmethanol and 40 ml of 5% lithium hydroxide may be added. The mixture isthen stirred, for example, at room temperature for 5 hours. Methanol isthen evaporated under reduced pressure and the aqueous solution is thenmade acidic by addition of dilute hydrochloric acid. The precipitate isfiltered, washed with water, and then dried. Recrystallization fromwater produces white crystals of 4-diethylphosphonatomethyl benzoicacid, of which the chemical formula is shown in FIG. 5C.

4-diethylphosphonatomethyl benzoic acid is then added to anhydrousdichloromethane. For example, 5.0 grams of 4-diethylphosphonatomethylbenzoic acid may be added to 50 ml of anhydrous dichloromethane. Excessamount of oxalyl chloride is added to this solution. A trace amount ofN,N-dimethylformamide is then added to the solution. The mixture may bestirred, for example, under nitrogen for 4 hours. The solvent and theexcess oxalyl chloride is then evaporated under reduce pressure toproduce a colorless oil, which is 4-diethylphosphonato-methyl benzoicacid, of which the chemical formula is shown in FIG. 5D.

4-diethylphosphonato-methyl benzoic acid thus obtained in the form ofthe colorless oil is then dissolved in anhydrous dichloromethane. Thesolution is then added to a solution of 2-nitrobenzyl alcohol indichloromethane containing triethylamine. The chemical structure for2-nitrobenzyl alcohol is shown in FIG. 5. After stirring 4 hours at roomtemperature, the solution is washed with 5% sodium bicarbonate, dilutehydrochloric acid and brine successively, and then dried over anhydrousmagnesium and filtered. The solvent is then evaporated under reducedpressure and solid residue is crystallized from ethanol to give aphosphonate ester. The ester is dissolved in anhydrous dichloromethaneand treated with 4 equivalent of bromotrimethylsilane, and then stirredunder nitrogen for 5 hours. Methanol and a few drops of hydrochloricacid is added and stirring may be continued for additional 1 hour. Theprecipitate is filtered and washed with ether, dried and crystallizedfrom ethanol to form photosensitive phosphonic acid as white crystals.

The chemical structure of the photosensitive phosphonic acid is obtainedfrom the chemical structure of FIG. 7 by replacement of R with ahydrogen atom, i.e., by substituting H— for R in FIG. 7.

The above procedure may be performed with the replacement of the2-nitrobenzyl alcohol with 4-trifluoromethyl-2-nitrobenzyl alcohol. A4-substituted photosensitive phosphonic acid, in which R in FIG. 7 isreplaced with CF₃—, is obtained by this process. Purification of thiscompound may be performed through crystallization from ethanol.

Further, the above procedure may be performed with the replacement ofthe 2-nitrobenzyl alcohol with 4-hexadecyloxy-2-nitrobenzyl alcohol.Another 4-substituted photosensitive phosphonic acid, in which R in FIG.7 is replaced with C₁₆H₃₃O—, is obtained by this process. Purificationof this compound may be performed through crystallization fromtoluene-ethanol mixture.

In general, various alcohol may be employed to produce variousphotosensitive phosphonic acid. R may be one of hydrogen, fully orpartially fluorinated alkyl, fully or partially fluorinated alkoxy, orfully or partially fluorinated alkylthio, and wherein a total number ofcarbon atoms in said alkyl, alkoxy, or said alkylthio is from 1 to 20.

Referring to FIG. 8, an unsubstituted or 4-substituted photosensitivephosphonic acid as covalently bonded to a metal M on the surface of ametal oxide is shown. Two oxygen atoms bond to the metal oxide andprovide a hydrophobic surface as R is exposed on the outside of themonolayer 200 (See FIG. 1). The end group of the unsubstituted or4-substituted photosensitive phosphonic acid is phosphonic acid has theformula PO(OH)₂. During bonding to the oxide surface, the end grouploses two hydrogen atoms. Thus, two oxygen atoms form a covalent bondwith the metal atom or the semiconductor atom of the oxide on thesurface.

Referring to FIG. 9, a derivative of the unsubstituted or 4-substitutedphotosensitive phosphonic acid after exposure to ultraviolet radiationis shown in which the CO—O—CH₂ bond in the photosensitive phosphonicacid is broken to provide a CO—OH termination, which provideshydrophilicity. Thus, the derivative of the unsubstituted or4-substituted photosensitive phosphonic acid as covalently bonded to themetal M on the surface of the metal oxide provides a hydrophilic surfacesince —OH is exposed on the outside of the second contiguous region 320of the monolayer 200.

Embodiment 2 Synthesis of Photosensitive Hydroxamic Acids

According to embodiment 2, or a second embodiment, of the presentinvention, 2-nitrobenzyl alcohol, of which the structural formula isshown in FIG. 10A, is added to a solution of phosgene. The solution ofphosgene may be generated by heating a solution of diphosgene intetrahydrofuran in the presence of activated charcoal. The mixture of2-nitrobenzyl alcohol and the phosgene solution is stirred, for example,at room temperature for 4 hours. The solvent and excess phosgene isevaporated under reduced pressure and an oily residue is obtained, whichis nitrobenzyloxycarbonyl chloride, of which the chemical formula isshown in FIG. 10B. The nitrobenzyloxycarbonyl chloride in the form ofthe oily residue is used without further purification in the next step.

A solution of 2-nitrobenzyloxycarbonyl chloride in anhydrous ether isadded to a solution of 4-aminomethylbenzoic acid in lithium hydroxide.For example, 5 mmole of 2-nitrobenzyloxycarbonyl chloride in 40 ml ofanhydrous ether is added with stirring to a solution of4-aminomethylbenzoic acid in 50 ml of 5% lithium hydroxide. Thestructural formula for 4-aminomethylbenzoic acid is shown in FIG. 11.

The mixture is thereafter stirred, for example, for additional 2 hours.Ether is evaporated and the aqueous solution is acidified with dilutehydrochloric acid. The precipitate is filtered, washed with water, andthen dried. Crystallization from ethanol produces a carbamate in theform of white crystals, of which the chemical formula is shown in FIG.12.

A 2 molar solution of oxalyl chloride in 10 ml dichloromethane is addedto a suspension of 10 mmole carbamate in 50 ml of anhydrousdichloromethane containing traces of N,N-dimethylformamide. The solutionis stirred for 4 hours, and then the solvent and excess oxalyl chlorideis evaporated under reduced pressure. An oily residue therefrom isdissolved in anhydrous 20 ml of dichloromethane, and added to a solutionof O-trimethylsilylhydroxylamine (12 mmole) and triethylamine (20 mmole)in 50 ml of dichloromethane. The solution is then stirred for 2 hours,washed successively with dilute hydrochloric acid and brine, dried overanhydrous magnesium sulfate, and evaporated. The residue is dissolved in20 ml of methanol, and 1 ml of trifluoroacetic acid is added and stirredfor 6 hours. The precipitate is filtered and washed several times withwater and then dried. Crystallization from ethanol affords thephotosensitive hydroxamic acid.

The chemical structure of the photosensitive hydroxamic acid is obtainedfrom the chemical structure of FIG. 13 by replacement of R with ahydrogen atom, i.e., by substituting H— for R in FIG. 13.

The above procedure may be performed with the replacement of the2-nitrobenzyl alcohol with 4-trifluoromethyl-2-nitrobenzyl alcohol. A4-substituted photosensitive hydroxamic acid, in which R in FIG. 13 isreplaced with CF₃—, is obtained by this process.

Further, the above procedure may be performed with the replacement ofthe 2-nitrobenzyl alcohol with 4-hexadecyloxy-2-nitrobenzyl alcohol.Another 4-substituted photosensitive hydroxamic acid, in which R in FIG.13 is replaced with C₁₆H₃₃O—, is obtained by this process.

In general, various alcohol may be employed to produce variousphotosensitive hydroxamic acid. R may be one of hydrogen, fully orpartially fluorinated alkyl, fully or partially fluorinated alkoxy, orfully or partially fluorinated alkylthio, and wherein a total number ofcarbon atoms in said alkyl, alkoxy, or said alkylthio is from 1 to 20.

Referring to FIG. 14, an unsubstituted or 4-substituted photosensitivehydroxamic acid as covalently bonded to a metal M on the surface of ametal oxide is shown. Two oxygen atoms bond to the metal oxide andprovide a hydrophobic surface as R is exposed on the outside of themonolayer 200 (See FIG. 1). The end group of the unsubstituted or4-substituted photosensitive hydroxamic acid has the formula CONHOH.During bonding to the oxide surface, the end group loses a hydrogenatom. Thus, an oxygen atoms form a covalent bond with the metal atom orthe semiconductor atom of the oxide on the surface.

Referring to FIG. 15, a derivative of the unsubstituted or 4-substitutedphotosensitive hydroxamic acid after exposure to ultraviolet radiationis shown in which the CH₂—NH—CO bond in the photosensitive hydroxamicacid is broken to provide a CH₂—NH₂ termination, which provideshydrophilicity. Thus, the derivative of the photosensitive hydroxamicacid as covalently bonded to the metal M on the surface of the metaloxide provides a hydrophilic surface since —OH is exposed on the outsideof the second contiguous region 320 of the monolayer 200.

EXAMPLES OF SELF-ASSEMBLY AND PHOTOPATTERNING Example I

A silicon substrate with 10 nm of hafnium oxide was cleaned by oxygenplasma and immersed in a 1 mmolar solution of unsubstitutedphotosensitive phosphonic acid in ethanol. After 4 hours, the sample wasremoved and washed with ethanol and dried. Contact angle measurementshowed a contact angle of average 80 degree with water. The sample wasthen exposed to ultraviolet light of 254 nm wavelength for half an hourand washed with ethanol and dried with stream of nitrogen. The contactangle had changed to average of 20 degree. The sample was immersed in anaqueous dispersion of CNTs in 1% sodium dodecyl sulfonate and dried. Anatomic force micrograph of the ultraviolet-exposed sample, as shown inFIG. 16A, shows relatively high density of carbon nanotubes on thesurface, whereas an atomic force micrograph of the unexposed sample, asshown in FIG. 16B, does not contain any carbon nanotube.

Example II

Selective placement of carbon nanotubes (CNTs) was demonstrated inanother test. A silicon wafer coated with 10 nm of hafnium oxide wascleaned with oxygen plasma and then immersed in a 1 mmolar solution of4-trifluoromethyl photosensitive phosphonic acid in ethanol for 4 hours.The sample was removed and washed with ethanol and dried under stream ofnitrogen. The sample was then exposed through a mask with 5 micrometerpitch to ultraviolet light for half an hour. After rinsing with ethanol,a solution of hydroxamic acid-functionalized carbon nanotubes inmethanol was drop cast on the sample, dried, and then rinsed withmethanol. Carbon nanotubes were selectively placed on the exposed areasof the monolayer. Scanning electron micrographs shown in FIGS. 17A and17B revealed that the monolayer was patterned with 5 micrometer lines,in which the carbon nanotubes are preferentially attached to the exposedregion, while the center of the unexposed regions are free of carbonnanotubes.

Example III

A silicon wafer with 10 nm of hafnium oxide was cleaned by oxygen plasmaand then immersed in a 0.5 mmolar solution of 4-trifluoromethylphotosensitive phosphonic acid for 8 hours. The sample was removed,washed with and ethanol successively, and dried by slow stream ofnitrogen. The sample was exposed through a mask with 5 micrometer pitchto 254 nm ultraviolet radiation for 30 minutes. After the exposure, thesample was washed with chloroform and ethanol successively, and driedunder nitrogen.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A material comprising: a metal; and a self-assembled monolayercomprising a photosensitive compound represented by the formula

wherein R is one of hydrogen, a fully or partially fluorinated alkyl, afully or partially fluorinated alkoxy, or a fully or partiallyfluorinated alkylthio, and wherein a total number of carbon atoms insaid alkyl, alkoxy, or said alkylthio is from 1 to
 20. 2. The materialof claim 1 wherein said metal is located on a surface of a metal oxide.3. The material of claim 1 wherein said total number of carbon atoms insaid alkyl, alkoxy, or said alkylthio is from 1 to
 10. 4. The materialof claim 3 wherein said total number of carbon atoms in said alkyl,alkoxy, or said alkylthio is from 1 to
 5. 5. The material of claim 1wherein R is H.
 6. The material of claim 1 wherein R is a fully orpartially fluorinated alkyl.
 7. The material of claim 1 wherein R is afully or partially fluorinated alkoxy.
 8. The material of claim 1wherein R is a fully or partially fluorinated alkylthio.
 9. The materialof claim 1 wherein said metal is covalently bound to said self-assembledmonolayer at said PO(OH)₂ end group by replacing said H atoms in saidPO(OH)₂ end group.
 10. A material comprising: a metal; and aself-assembled monolayer comprising a photosensitive compoundrepresented by the formula:

wherein R is one of hydrogen, fully or partially fluorinated alkyl,fully or partially fluorinated alkoxy, or fully or partially fluorinatedalkylthio, and wherein a total number of carbon atoms in said alkyl,alkoxy, or said alkylthio is from 1 to
 20. 11. The material of claim 10wherein said metal is located on a surface of a metal oxide.
 12. Thematerial of claim 10 wherein said total number of carbon atoms in saidalkyl, alkoxy, or said alkylthio is from 1 to
 10. 13. The material ofclaim 12 wherein said total number of carbon atoms in said alkyl,alkoxy, or said alkylthio is from 1 to
 5. 14. The material of claim 10wherein R is H.
 15. The material of claim 10 wherein R is a fully orpartially fluorinated alkyl.
 16. The material of claim 10 wherein R is afully or partially fluorinated alkoxy.
 17. The material of claim 10wherein R is a fully or partially fluorinated alkylthio.
 18. Thematerial of claim 10 wherein said metal is covalently bound to saidself-assembled monolayer at said HOHN end group by replacing one of saidH atoms of said HOHN end group.